The method of non-linear ultrasound as a tool for the non-destructive inspection of structural epoxy-metal bonds—a résumé

The method of non-linear ultrasound (NLUS) is frequently discussed as a promising non-destructive inspection tool to detect the deteriorating effect of operational loading on the performance of structural adhesive metal bonds. The non-linear component in the ultrasound pulse propagating across the joint arises in the weakest region of the adhesive. As the weakest region limits the mechanical strength of the bond a correlation between the ultrasonic-mechanical deformation behaviour and the bond strength is expected. This paper reports on efforts to verify such a correlation for epoxy–aluminium bonds undergoing practice relevant hydrothermal or mechanical loading. In conclusion, no corresponding NLUS signal is measured although the joints are aged significantly or strained up to fracture.